Slip‐Rate on the Main Köpetdag (Kopeh Dagh) Strike‐Slip Fault, Turkmenistan, and the Active Tectonics of the South Caspian

Abstract

We provide the first measurement of strike‐slip and shortening rates across the 200‐km‐long right‐lateral strike‐slip Main Köpetdag Fault (MKDF) in Turkmenistan. Strike‐slip and shortening components are accommodated on parallel structures separated by ∼10 km. Using Infra‐red‐stimulated luminescence and reconstruction of offset alluvial fans we find a right‐lateral rate of 9.1 ± 1.3 mm/yr averaged over 100 ± 5 ka, and a shortening rate of only ∼0.3 mm/yr averaged over 35 ± 4 ka across the frontal thrust, though additional shortening is likely to be accommodated locally by folding and faulting, and regionally within the eastern Caspian lowlands to its south. The MKDF is estimated to have ∼35 km of cumulative right‐lateral slip which, if these geological measurements are correct, would accumulate in only 3–5 Ma at the rate we have determined, suggesting that the present tectonic configuration started within that time period. We use the MKDF slip‐rate to form a velocity triangle, from which we estimate the Iran‐South Caspian and Eurasia‐South Caspian shortening rates, and show that the South Caspian Basin moves at 10.4 ± 1.1 mm/yr in direction 333° ± 5 relative to Eurasia and at 4.8 ± 0.8 mm/yr in direction 236° ± 14 relative to Iran. In contrast to both the eastern Köpetdag and the Caspian lowlands the MKDF has little recent or historical seismicity. The rapid slip‐rate estimated here suggests that it is a zone of high earthquake hazard.

Strain and Moment Rates from GPS and Seismological Data in Northern Iran: Implications for an Evaluation of Stress Trajectories and Probabilistic Fault Rupture Hazard

“…The Kopeh Dagh range, as the eastern continuation of the Alborz-Talesh range, includes Tertiary and Mesozoic sediments, which have been folded during the Oligo-Miocene orogeny [36,37]. The Kopeh Dagh Fault system, with a slip rate of 9.1± 1.3 mm/yr, is characterized as the NW-boundary of the range [38].…”

“…In the Alborz range, after the Pliocene (3-5 Ma), oblique shortening is partitioned into pure thrust and pure strike-slip [42,47]. The motion of the SCB relative to both Eurasia (10.4 +/− 1.1 mm/yr in direction 333 • +/− 5) and central Iran (4.8 +/− 0.8 mm/yr in direction 236 • +/− 14) enhances westward underthrusting of the basin beneath the Talesh mountains of Iran and Azerbaijan [38,42,48]. The general wrenching of the belt was dependent on these motions, which in some parts have led to the normal component of some faults (e.g., Sari, Firouzkuh, and Astaneh faults) [49,50].…”

An InSAR‐GNSS Velocity Field for Iran

“…Rizza et al, 2013;Su et al, 2016). A similar East velocity change is observed at ∼55°E, with overall positive velocities in Turkmenistan and northeastern Iran changing to negative velocities East of the South Caspian, consistent with 6-10 mm/yr of right-lateral motion along the Main Kopet Dagh Fault (MKDF) and 4-6 mm/yr left-lateral motion along the Sharoud Fault Zone (SFZ) (Dodds, 2021;Walker et al, 2021). Between 57°-60°E, we observe a small 1-2 mm/yr East velocity change across the Doruneh Fault (DF), consistent with left-lateral slip along the fault (Farbod et al, 2016;Pezzo et al, 2012;Walpersdorf et al, 2014), which is masked by the Dasht-e Kavir to the west and becomes negligible East of 60°E.…”

Probing the Upper End of Intracontinental Earthquake Magnitude: A Prehistoric Example From the Dzhungarian and Lepsy Faults of Kazakhstan

“…Earthquake ruptures in continental interiors can be complex, and there are several examples that show the potential for very large earthquakes to occur on a network of multiple short faults, which may be of particular importance for rupture within diffuse networks of critically stressed faults, as commonly observed in plate‐interior settings (Abdrakhmatov et al., 2016; Ainscoe et al., 2019; King et al., 2019; Ross et al., 2019). More fundamentally, there is uncertainty in (a) the degree to which the recent and historical records of earthquakes encompass the maximum likely magnitude of future events (Hu et al., 2021; Pierce et al., 2021; Walker et al., 2021), and (b) the relationships between rupture length, average and maximum surface slip, and magnitude (Leonard, 2010; Manighetti et al., 2007; Ou et al., 2020; Thingbaijam et al., 2017; Wesnousky, 2008).…”